The invention relates to hinges, especially piano type hinges which are used to mount a swinging door to a fixed door frame. Such doors may be made of any suitable material, such as wood, plastic, or metal, and the hinges may be made of any appropriate material, including plastic or metal, such as aluminum, steel or brass.
More particularly, the invention is in a magnetic device for monitoring the opening and closing of a door as it swings to and from a closed position in a fixed door frame to which the door is mounted.